Solubility Product

The solubility product, Ksp, is the equilibrium constant for a solid substance dissolving in an aqueous solution. It represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the Ksp value it has.

In order for a salt to precipitate out the product of each of the ions has to exceed the solubility product.

For example,the Ksp of silver sulfate would be the product of 2 ions of silver and one ion of sulfate – Ksp = [Ag+]2[SO42-].

Write the equilibrium equation for the changes that happen in a saturated solution of strontium sulfate in the presence of some solid.

2. Work out the concentration of the dissolved strontium ions in mol dm-3.

Molarity = 5.66*10-4

3. If you added some sodium sulfate solution to a saturated solution of strontium sulfate, what would you expect to happen to the concentration of dissolved strontium ions? Explain your answer.

If there is a saturated solution of strontium sulfate a precipitate will form as soon as a soluble sulfate is added. This is due to the fact that the Ksp is a product of both the cation and the anion and thus when the concentration of one of the ions is increased, the saturation point is reached at a lower concentration of the insoluble salt and therefore this would precipitate out.

4. Suppose the concentration of the sulfate ions in the mixture was 0.50 mol dm-3 (virtually all of which is due to the ions from the sodium sulfate), work out the new concentration of the strontium ions after the addition of the sodium sulfate solution.